1. Field of the Invention
This invention relates to an image forming system to be used in reproducing on a recording paper an image recorded on a microfilm.
2. Description of the Related Art
The microfilm to be used in the reader printer is either a positive film or a negative film, depending on the occasion. FIG. 15 is a diagram illustrating part of a microfilm M of the type to be taken up in the form of a roll. The microfilm M shown in this diagram contains in each of the image information frames F a negative image consisting of an image information A such as a letter recorded in a transparent figure in the frame and the remainder in a black (dark) background as indicated by hatching. The part of the microfilm M surrounding the image information frames F and excepting marks B for retrieval such as blip marks or document marks is transparent.
When the information A recorded in the form of a negative image as described above is to be reproduced on a recording paper, the transparent part of the image information A is reproduced in a positive figure on the recording paper by reversal development using an electrophotographic image forming apparatus provided with a photosensitive element. When the transparent background part of the microfilm M surrounding the image information frames F is exposed to the light directed to the photosensitive element during the reproduction of the recorded image on the recording paper, this part is formed in a black figure on the recording paper not only to impair the appearance of a printed image but also to increase the consumption of the toner.
In case where the negative image formed on the microfilm M as illustrated in FIG. 15 is to be reproduced on the recording paper, an effective measure must be taken to keep the part G of film surrounding the rectangular image information from F and containing no recorded image (hereinafter referred to as "background part of film"), namely the background part G of film outside the border line E between the image information frame F and the background part G of film, from being reproduced on the recording paper. Owing to this measure, since the image information A is exclusively reproduced on the recording paper, the consumption of the toner can be decreased and the appearance of the printed image can be improved as well.
An act of accurately masking the part of the film outside the border line E for the purpose of keeping the background part G of the film outside the border line E, however, is difficult to fulfil on account of the limitation imposed on the accuracy with which a masking device is positioned relative to the border line E. To overcome this difficulty, the accuracy with which the sensor serving the purpose of detecting the masking position must be improved to the order of microns. The concept of accurately masking the background part G of film is impracticable in the light of the cost of the photosensor itself and the increase of cost due to intrication of the control circuit part required for processing image information from the photosensor.
In an effort to realize the decrease of the consumption of the toner and the improvement of the print quality within the purview of practicability, an idea has been conceived to effect detection of the position of the edge of an image information frame by the use of a photosensor having light-receiving elements arrayed at intervals of mm. When the image in the image information frame is reproduced on the recording paper while the image to be reproduced is regulated with the masking device accurately to the detected position of the edge of the image information frame, there arises the possibility that the background part of the film will partially remain in the form of a rectangular frame in the reproduced image. The reason for this possibility is that the portion of the border line E illustrated in FIG. 15 deflects from the edge of the image information frame detected by the photosensor with a margin short of the detecting pitch of the photosensor. To ensure perfect prevention of the appearance of this rectangular frame in the image reproduced on the recording paper, it is necessary and sufficient to erase the relevant region by means of such a masking device as a shutter so that the external image inclusive of the margin short of the detecting pitch from the position at which the edge of the image is detected will not be reproduced. Where the information recorded is so expansive as to reach closely to the border line E of FIG. 15, however, there arises the possibility that the act of masking the film surface as far as the position inclusive of the aforementioned detecting pitch of the photosensor to attain perfect erasure of the rectangular frame will entail unwitting erasure of the recorded image information.
U.S. Pat. No. 4,839,696 discloses an invention for solving the problem described above by converting the image information detected with the photosensor into binary data and developing the binary data in the form of a matrix thereby allowing detection of the position of the border line E, namely the position of the rectangular frame, of the image information frame. Where the information is recorded so expansively as to reach closely to the border line E, the operator controls the operation of the apparatus so that the actual background part of the film will be partially formed on the recording paper, i.e. the background part of the film will be allowed to remain in the form of a frame and the recorded information will be reproduced safely in its complete form. Where the information is not recorded so expansively as to reach closely to the border line E, the idea of attaining perfect erasure of the background part of film surrounding the image by masking the film to the extent of even covering the edge of the image region has been put to trial.
Incidentally, the technique disclosed in the U.S. patent specification betrays inferior operability of the reader printer because it compels the operator to perform the key operation while keeping a constant watch on the image projected on the screen.
Further, the technique of this U.S. patent specification has the problem of entailing the possibility that since the detection of the contour portion of the image information frame or the position of the border line is attained by starting the detection of the image information frame from the edge part of the frame with the aforementioned photosensor, the detection of the range of the image to be reproduced on the recording paper will consume much time and the photosensor will produce an erroneous operation in the presence of a blip mark B or dust.
When the reader printer is used in copying an image recorded on the microfilm, generally the procedure which comprises first projecting recorded images one by one on the screen, retrieving the particular image desired to be copied, and thereafter starting the work of copying is employed more often than not. It naturally follows that the image retrieved and readied for copying is positioned in the central part of the screen by the operator's control of the operation of the reader printer. When the copying work is started in the ensuant state of the reader printer, the recorded image is scanned against the photosensitive element.